Studies are in progress in the following areas: (1) the mechanism of action of 2-keto-4-hydroxyglutarate aldolase, an important enzyme in the metabolism of L-hydroxyproline by mammals which has been found to have many novel properties not observed in the study of other aldolases. Such efforts will include an examination of the steady-state kinetics of the catalyzed reaction and also an exploration of the functional groups in the enzyme molecule which participate in the catalytic process. (2) the subunit structure and properties of pure 2-keto-4-hydroxyglutarate aldolase. (3) the occurrence, properties, and role of this coupled sequence of metabolic reactions, as catalyzed by enzymes in brain or bacteria: gamma- hydroxyglutamic acid yields CO2 plus alpha-hydroxy- gamma-aminobutyric acid; malic acid yields malic acid semialdehyde.